This application claims the priority of Japanese Patent Application No. 10-42837 filed on Feb. 9, 1998 which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an electronic endoscope system, and more specifically to an electronic endoscope system which is configured as a whole so as to be capable of ensuring a predetermined brightness with a halogen lamp in particular used as a light source.
2. Description of the Prior Art
An electronic endoscope system supplies rays from a light source such as a xenon lamp or a halogen lamp to a tip of an electronic endoscope through a light guide and captures an internal image of an object to be observed with an image pickup device, for example, a CCD (charge coupled device) by projecting the rays from the tip into the object to be observed. Video signals which are to be used, for example, as odd field data and even field data are sequentially read from the CCD, subjected to processing such as amplification, white balance and gamma compensation, and are stored in a memory. The video signals are then read out of the memory to display an internal image of the object to be observed on a monitor or the like.
FIG. 5 shows a condition for reading out field signals from the CCD mentioned above. Accumulated electric charges (corresponding to picture elements) are read out from the CCD generally at intervals of a vertical synchronous period (field period) of 1/60 second. Odd field signals and even field signals are read out alternately, for example, as shown in FIG. 5: an odd field signal (data) for a period of n+1 (1/60 second), an even field signal for a period of n+2, an odd field signal for a period of n+3 and an even field signal for a period of n+4.
Though electric charges on odd lines and even field lines of the CCD can be read out as odd field signals and even field signals respectively, the color-difference line sequential mixture readout system adds electric charges accumulated on an upper line to those accumulated on a lower line, thereby reading out mixture signals of (0+1) line, (2+3) line, . . . , for example, as odd field signals and mixture signals of (1+2) line, (3+4) line, . . . as even field signals.
The field signals of the periods n+1 and n+2 are used to form an n+first frame, whereas the field signals of the periods n+3 and n+4 are used to form an n+second frame, whereby an internal image of an object to be observed is displayed on the monitor by interlace scanning of these field signals.